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Microsoft Patches Critical Flaw in Malware Protection Engine

The emergency update addressed CVE-2018-0986, which would let an attacker execute malicious code on a Windows machine.

Microsoft has issued an emergency patch for CVE-2018-0986, a remote code execution vulnerability in the Microsoft Malware Protection Engine (MMPE). Security researcher Thomas Dullien, with Google's Project Zero, is credited with finding the bug, Microsoft reports.

MMPE, or mpengine.dll, provides scanning, detection, and cleaning capabilities for Microsoft's antivirus and antispyware software. Microsoft typically issues MMPE updates once a month, or as needed, to protect against new threats.

This critical vulnerability exists when MMPE doesn't properly scan a specially crafted file, which leads to memory corruption. If successfully exploited, this could let an attacker execute malicious code on a target machine; take control of the system and install programs; view, change, or delete data; or create new accounts with full user rights.

An affected version of MMPE needs to scan a specially crafted file in order for the bug to be exploited. There are a few ways an attacker could make this happen, Microsoft explains in a security advisory, and he or she doesn't need to be technically advanced to do it.

One way is to conceal the files on a website the victim visits. Another is to send the file via email or instant messenger. Alternatively, an attacker could abuse a website that hosts user-provided content by uploading the specially crafted file to a shared location.

MMPE will automatically scan files if the user's anti-malware software has real-time protection enabled, so the vulnerability can be exploited without the user doing anything. If real-time scanning is not enabled, an attacker would have to wait for a scheduled scan in order to exploit.

"All systems running an affected version of antimalware software are primarily at risk," Microsoft says. This update fixes the bug in MMPE version 1.1.14700.5 by adjusting how MMPE scans specially crafted files. In addition to the changes for this particular flaw, the patch also includes defense-in-depth updates "to help improve security-related features," Microsoft says.

Administrators and users don't need to take action to install MMPE updates because they're automatically applied within 48 hours of the patch's release. The exact time of deployment will depend on your software, Internet connection, and infrastructure configuration.

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